Characterization of the SIRT genes and their distinct expression patterns in Manila clams (Ruditapes philippinarum) exposed to air

Abstract

Silent information regulator 2 family proteins (sirtuins) are members of a highly conserved family of deacetylases found in organisms ranging from bacteria to human beings, functioning as a molecular chain to transmit cell energy and regulate the cell cycle. Seven members of the human sirtuin family have been identified, which are named as SIRT1–SIRT7. They all have a highly conserved NAD+ binding domain and a catalytic domain, and their specific N- and C-terminals enable their substrate specificity. In this study, five sirtuin genes, named SIRT1, SIRT2, SIRT4, SIRT6 and SIRT7, were identified in the Manila clam Ruditapes philippinarum. Phylogenetic analysis showed that the R. philippinarum SIRT proteins could be grouped into three clusters and were closely related to their counterparts in other species of molluscs. The RpSIRT genes were differentially expressed across different developmental stages and at various tissues of the Manila clams. SIRT1 expression increases with the developmental stage, indicating that SIRT1 might play a key role in the early developmental stage of clam through regulating the cell cycle and energy metabolism of clam growth. For the spatial expression patterns of all the five SIRT genes investigated, the expression level of the SIRT1 gene in gonad was the highest, consistent with what was reported in Sparus aurata. In addition, the RpSIRT genes also responded to air exposure and low temperature stresses. After exposure to air, expression levels of the SIRT-1, SIRT-2, SIRT-6 and SIRT-7 genes (except for SIRT4) were increased significantly (P < 0.05). After 24 h of air exposure, expression levels of SIRT1 and SIRT2 in the low temperature group were significantly higher than those in the normal temperature group (P < 0.05), implying that prolonged air exposure might alter the metabolic pattern of clams dominated by aerobic pathway at low temperature. Our results suggest that the Ruditapes philippinarum SIRT genes might play important roles in regulating the level of NAD+/NADH in cells, and therefore might regulate the redox pathway of energy metabolism in clams during air exposure, which might eventually improve their antioxidant capacity.